John Bradley tells THR his character, Samwell Tarly, goes from likable nice guy to someone whose actions may irreparably harm the people he loves.

John Bradley as Sam

Last season, Samwell Tarly (John Bradley) began making the transition from frightened boy to (relatively) brave man. He killed a White Walker and safely ushered his love interest Gilly and her son back to Castle Black.

"There are moments early on in season four where certain parts of Sam's neuroses and his paranoia and some of the less appealing aspects of his personality come to the fore for the first time," Bradley says. "For the first time we see him make some pretty selfish, self-centered decisions that are beneficial to nobody and could be utterly catastrophic."

Read what else Bradley had to say about his character and Game of Thrones' upcoming fourth season below.

Sam got to be a hero in season three. Where is he when we pick up with him?

Sam is the absolute last person to acknowledge how brave he is. Ever since he's made his first appearance, the audience has been aware of something inside of him – some kind of worth – but I think Sam is always going to be the last person to acknowledge that. It was nice to see Sam's bravery take him by surprise.

Going into season four, Sam senses his own self-worth. He demands more respect from those around him. Whether he gets that, that's a different matter.

Are there changes in store for Sam this season?

When I first read these scripts for season four, there were parts in it where you see Sam in a different light than you've ever seen before. There are moments early on in season four where certain parts of Sam's neuroses and his paranoia and some of the less appealing aspects of his personality come to the fore for the first time. For the first time we see him make some pretty selfish, self-centered decisions that are beneficial to nobody and could be utterly catastrophic.

After killing a White Walker, Sam has returned to Castle Black to warn people about what he's seen. Does that get him more respect?

Because he's done something so outlandish, and something nobody thought was possible, people at Castle Black are reluctant to believe it. If Sam would have killed a bunch of Wildlings, they'd be slightly more likely to believe that because it'd be a more realistic achievement.

It must be nice for Sam to be reunited with Jon Snow. What's that like, getting to work with his good friend again?

When we go into season four, he's done what nobody thought was possible and gotten Gilly back to Castle Black. He's also got Jon back at Castle Black. To have the three people he cares most about in the world – if you count baby Sam – all in the same place, he can't believe his luck.

Sam is somebody who finds happiness very hard to come by. He's so unfamiliar with happiness that I don't think he knows how to react to it properly.

When you were cast in Thrones, you hadn't read the books. Do you read them now?

I have read all the books now. I read them between seasons two and three. I wanted to wait until the show was established and every actor -- including myself -- had absolute ownership of their parts and the show had become an entity all of its own.

What do you think of them?

It was strange to see a character you had become so familiar with grow independently of you. You think you own a character and you realize it has a whole other life you haven't even thought about yet.

What's something you've learned from the older actors that you get to work with?

When we shot season one, I'd done absolutely no TV work before. In a set that huge with so many people doing so many jobs, you can feel a little bit lost. That's why it was always beneficial to have older actors like James Cosmo (Jeor Mormont), Owen Teale (Alliser Thorne) and Peter Vaughan (Maester Aemon) around – these guys who have done absolutely everything – who have worked with the best and turned themselves into the best. You can't help but learn from these people. You can't help observing absolute masters of their trade at work.

At the end of the day when you're done working, do you go back into modern life or do you have to stay in that world mentally?

The stakes are so high in the world of Game of Thrones and the consequences are so brutal and unsavory at times, if you try to immerse yourself in it too much you'll drive yourself crazy. You have to do something that will keep you in touch with who you are and who you're working with. That's very easy to do with Kit [Harington] and everyone else I work with. They all see the importance of keeping a happy ship.

So they'll be times you and Kit will share a laugh on set.

Yes, but you absolutely do that on your own time. You can't do that on anybody else's time. You can't do it when there are thousands of dollars being wasted a minute. You don't want to be the one doing that.

George R.R. Martin has said he's the most like Sam of all of his characters. Does that get you any special treatment?

I think what he said was, he wishes he was like Tyrion, but in reality he's actually more like Sam. I don't know if that means Sam is the part of himself that he is but doesn't want to be. That might mean Sam doesn't get any preferential treatment at all. He might want to exorcize the ghost of Sam sometimes.

If you take a character who is an inherently likable person with a lot of good qualities, it's always good drama to see those people get a spear through the face at some point. That's what George does. It seems like George only writes likable characters to kill them off at some point. While I'm trying to make Sam as endearing as I possibly can, I might be signing my own death warrant.

So many of the characters in Thrones are really well developed. Why is that?

No characters on TV have really developed so much over 10 hours. Something like Breaking Bad – which was done at such a breakneck speed, and it was brilliantly consistent at keeping the twists coming – that's the only show I can think of where change happens so quickly, and characters are never in a psychological state very long. They are constantly evolving to match what is happening. Game of Thrones is kind of like that as well.